JP7187697B2 - Catalytic device for lead-acid battery and lead-acid battery - Google Patents

Description

The present invention provides a catalytic device for lead-acid batteries, more preferably for lead-acid batteries, which can prevent electrolyte solution depletion, enable long life, and ensure safety even in the event of excessive gas flow. It relates to a catalytic device and a lead-acid battery including the catalytic device.

Lead-acid batteries, particularly automotive lead-acid batteries, generally employ an open structure that allows an electrolyte solution such as dilute sulfuric acid to flow freely. A lead-acid battery with such a structure generates oxygen and hydrogen gases when charged, and therefore includes vents (vent ports) for exhausting these gases. Otherwise, the gas pressure inside the battery will increase, which may lead to deformation and breakage of the battery.
Such gas leakage from the vent leads to depletion of the electrolyte solution. When the electrolyte solution is reduced, the chemical reaction of the battery becomes insufficient, resulting in a decrease in charge capacity and discharge capacity.
Various efforts have been made in the past to address these problems.

Patent Document 1 discloses a catalyst part for a lead-acid battery, comprising a catalyst layer containing a catalyst for accelerating a reaction to produce water or steam from oxygen and hydrogen, and at least one of water and steam. A configuration is disclosed in which parts condense and/or flow back into the interior of the battery. The catalytic portion reduces electrolyte solution depletion due to outgassing and leakage from the electrolyte solution, thereby providing a long life lead-acid battery.

US Pat. No. 5,300,009 discloses a catalytic device for recombination of decomposed gases from an electrolyte solution. This catalytic device has the ability to filter catalytic poisons (acidic electrolyte solutions) and control recombination temperature. More specifically, the catalytic device includes porous sections that allow gases, but not liquids, to pass through and prevent catalyst poisons (eg, acidic electrolyte solutions) from reaching the catalyst. Gases that have passed through the porous section are said to be able to reach the catalytic sites where they recombine and flow back through the porous section.
US Pat. No. 5,200,000 also discloses a catalyst device in which the heat of reaction of the catalyst causes the container to melt and physically cover the catalyst for cessation of catalytic action.

JP 2017-201594 A U.S. Pat. No. 7,326,489

As noted above, when a typical lead-acid battery is charged, it releases oxygen and hydrogen gas outwardly from the vents, depleting the electrolyte solution of the lead-acid battery. When the electrolyte solution is depleted, the chemical reaction of the battery becomes insufficient and the charge and discharge capacities are reduced. While not wishing to be bound by any particular theory, it is believed that increasing the concentration of dilute sulfuric acid in the electrolyte solution can corrode the positive plate and reduce capacity, and that decreasing the electrolyte solution level exposes the electrodes. This can cause the discharge capacity to drop rapidly, further corroding the joint between the negative plate and the strap.

In addition, depletion of electrolyte solution can also lead to sulfation and feedthrough shorts. Sulfation is a phenomenon in which the lead sulfate produced by the discharge is not sufficiently decomposed by the electrical charge into lead dioxide and lead to form bulk crystals of lead sulfate. Such bulk crystals, which are difficult to reduce to metallic lead, degrade battery performance and shorten battery life. Moreover, such bulk crystals also participate in feedthrough shorts. Bulk crystals grow on the electrodes into needle-like crystals called "dendrites". As dendrites continue to grow, they can reach the other electrode and cause a short circuit. This is a through short and the battery can no longer be charged and discharged.

In particular, in recent years, the use of idling-stop type automobiles has been increasing to improve fuel efficiency. Lead-acid batteries used in idling stop vehicles supply power to all devices such as air conditioners and fans during idling stop. Therefore, lead-acid batteries tend to be undercharged and used at a lower state of charge than conventional start-up lead-acid batteries, causing sulfation and feedthrough shorts. By preventing the electrolyte solution from depleting, sulfation and feedthrough short circuits can be prevented.

US Pat. No. 6,300,001 discloses a catalyst portion for reducing electrolyte solution depletion due to outgassing and leakage from the electrolyte solution. In other words, the oxygen and hydrogen gases generated from inside the lead-acid battery can be recombined by the catalyst to form water or water vapor and flow back into the battery. Water or water vapor formed by such recombination is present at or near the catalyst and is very unlikely to pose a safety concern (e.g. excessive gas flow causes excessive temperature rise). . However, it is useful to have additional safety measures in case of unforeseen circumstances.

US Pat. No. 6,300,000 discloses a catalytic device with a shutdown function. Specifically, the catalytic device container is melted by the heat of catalysis and physically covers the catalyst for catalysis termination. Therefore, once the stop function is activated, the catalyst is physically covered and no further catalysis can take place. Furthermore, after the container is melted, the catalyst in the container can leak into the electrolyte solution and short circuit. In WO 2005/010001 the shutdown function is provided in the container of the catalyst device, and furthermore the container is not adjacent to the catalyst. Therefore, it is expected that it will take a significant amount of time to transfer the heat of the catalyst to the vessel.
Furthermore, when the catalyst device of Patent Document 2 actually operates, it is necessary to control the temperature of the catalyst device of Patent Document 2 relatively high (about 70 to 90 ° C.), and the catalyst device is charged as a backup. However, it cannot be used in an environment where charging is performed discontinuously and the temperature cannot be controlled. For example, the device of Patent Document 2 is not necessarily used during continuous charging and is not suitable for automotive lead-acid batteries that may be used in cold climates.
The catalytic device of US Pat. No. 6,200,004 employs a microporous membrane that controls gas flow or allows only a small amount of gas to pass through to suppress the temperature rise of the catalyst. Therefore, water vapor generated in the catalytic device cannot escape efficiently and can easily be retained within the catalytic device. If the above temperature control is not performed, the water held in the device may solidify under a low temperature atmosphere such as 0 degrees Celsius or less, causing deformation or destruction of the casing of the catalyst device.

In view of the above situation, the object of the present invention is a catalytic device for lead-acid batteries, which can reduce electrolyte solution loss due to gas release and leakage from the electrolyte solution, Therefore, it is an object of the present invention to provide a catalytic device that provides a lead-acid battery that has a long life and can ensure safety even with an excessive flow of gas, and a lead-acid battery that includes the catalytic device.

The present invention provides the following aspects.

[1] A catalyst layer containing a catalyst for promoting a reaction for producing water or steam from oxygen and hydrogen, and a porous membrane containing a thermoplastic resin having a melting point or glass transition temperature of 160° C. or less. wherein at least one surface of the catalyst layer is in contact with the porous membrane, and the porous membrane has a planar size equal to or greater than the planar size of the catalyst layer A catalytic device characterized by having a planar size.
[2] The catalytic device according to item 1, wherein the porous membrane contains polyethylene.
[3] comprising at least two of said porous membranes, said porous membranes being laminated in contact with both planar surfaces of said catalyst layer, and optionally peripheral portions of said porous membranes being laminated to each other; 3. A catalytic device according to item 1 or 2.
[4] Any one of items 1 to 3, further comprising an expanded porous polytetrafluoroethylene membrane having a Gurley number of 100 seconds or more and being in contact with the porous membrane on the opposite side of the catalyst layer. A catalytic device according to any one of claims 1 to 3.
[5] The catalytic device according to any one of items 1 to 4, further comprising at least one porous membrane capable of absorbing or decomposing catalyst poisons.
[6] The porous membrane capable of absorbing or decomposing the catalyst poison contains a substance capable of absorbing or decomposing the catalyst poison inside the porous membrane capable of absorbing or decomposing the catalyst poison. 6. The catalytic device according to 5.
[7] The catalytic device according to item 5 or 6, wherein the porous membrane capable of absorbing or decomposing the catalyst poison comprises expanded polytetrafluoroethylene.
[8] Any one of items 1 to 7, further comprising a hydrophobic porous membrane located closer to the inside of the lead-acid battery than the catalyst layer, wherein the hydrophobic porous membrane has a Gurley number of 20 seconds or less. A catalytic device according to any one of claims 1 to 3.
[9] The catalytic device according to item 8, wherein the hydrophobic porous membrane comprises expanded polytetrafluoroethylene.
[10] A lead-acid battery comprising the catalyst device according to any one of items 1-9.

The present invention is a catalytic device for lead-acid batteries, which can reduce electrolyte solution depletion due to gas release and leakage from the electrolyte solution, thus having a long life and eliminating excess gas. Provided are a catalyst device that provides a lead-acid battery that can ensure safety even in a rough flow, and a lead-acid battery that includes the catalyst device.

FIG. 1 is a schematic diagram according to one aspect of the present invention. FIG. 2 is a conceptual diagram showing a catalyst carrier disposed within the cavity of the hydrophobic porous member or on the surface of the pores.

A catalyst device for a lead-acid battery provided by the present invention comprises a catalyst layer containing a catalyst that promotes a reaction for producing water or steam from oxygen and hydrogen, and a thermoplastic catalyst having a melting point or glass transition temperature of 160° C. or less. At least one surface of the catalyst layer is in contact with the porous membrane, and the porous membrane has a planar size equal to or greater than the planar size of the catalyst layer.

FIG. 1 schematically illustrates a catalytic device according to one aspect of the invention. One aspect of the invention is described with reference to FIG. FIG. 1 shows a schematic cross-sectional view of a catalytic device for a lead-acid battery. The bottom side of the figure is the inside of the battery and the top side of the figure is the outside of the battery. Underneath the catalytic device (inside the cell) is an electrolyte solution (not shown). Since the electrolytic solution of a lead-acid battery is a diluted sulfuric acid aqueous solution, the electrolytic solution (diluted sulfuric acid aqueous solution), sulfuric acid mist, moisture, and hydrogen gas and oxygen gas generated by battery reactions exist in the internal space of the battery.

When hydrogen gas and oxygen gas flow through a catalyst layer (1) containing a catalyst that promotes the reaction for producing water or steam from oxygen and hydrogen, the reaction to produce water or steam proceeds in the catalyst layer (1). . Hydrogen gas and oxygen gas generated by cell reactions recombine in the catalyst layer (1) to produce water or water vapor, which in some instances condenses and/or flows back into the cell interior. do. As a result, depletion of electrolyte solution in the battery is reduced.
The water produced in the catalyst layer (1) can be released in liquid form and in the form of water vapor. This is particularly advantageous when the battery is cycled on and off, as is the case with automotive batteries. The reason for this is that when a battery in operation is stopped, the temperature of the battery drops, and the water or steam generated up to that point tends to condense and become liquid. Water may not remain in the catalyst layer (1) since not only water vapor but also liquid can be released from the catalyst layer (1). Therefore, even if the atmospheric temperature is as low as less than 0 degrees Celsius, solidification of water in the catalyst layer (1), which may cause damage to the casing of the catalyst layer (1), etc., is prevented. In other words, use of the catalytic device of the present invention eliminates the need for temperature control to generate steam as in US Pat.

The catalyst device of the present invention includes a catalyst layer (1) and a porous membrane containing a thermoplastic resin having a melting point or glass transition temperature of 160° C. or less. Additionally, at least one surface of the catalyst layer is in contact with the porous membrane. Furthermore, the porous membrane has a planar size equal to or larger than the planar size of the catalyst layer.
The porous membrane is shown as porous membrane (2) in FIG. Hydrogen gas and oxygen gas generated in the cell reaction react with each other in the catalyst layer (1). This reaction is exothermic. When excessive amounts of hydrogen gas and oxygen gas flow into the catalyst layer (1) due to unexpected circumstances, the reaction in the catalyst layer (1) proceeds excessively, and the temperature of the catalyst layer (1) and its surroundings becomes excessive. may rise to In general, an increase in temperature results in enhanced catalyst activity, thus causing a further increase in reaction rate, which can lead to thermal runaway and ignition. In the present invention, at least one surface of the catalyst layer (1) is in contact with the porous membrane (2), and the porous membrane (2) is made of a thermoplastic resin having a melting point or glass transition temperature of 160° C. or lower. include. The catalyst layer (1) is in contact with the porous membrane (2), thereby allowing the heat of catalysis to readily transfer to the porous membrane (2). Therefore, the volume of the porous membrane (2) changes due to melting or glass transition at a temperature of 160° C. or less. Accordingly, the pores of the porous membrane (2) are further reduced in size or such pores are closed so that very little gas can rapidly pass through the porous membrane (2) and gas contacting it is It hardly flows into the catalyst layer (1) and suppresses the catalytic action. As a result, the heat of the catalytic action is rapidly lowered, and the temperature rise of the catalyst layer (1) and its surroundings is suppressed.
The melting point or glass transition temperature of the thermoplastic resin can be appropriately selected according to the amount of generated gas, catalytic performance, and the like. The melting point can be between 100°C and 180°C, and the glass transition temperature can be between 60°C and 160°C.
The thermoplastic resin can be polyethylene, polypropylene, polyvinyl chloride, polymethylmethacrylate, polystyrene or polyvinylidene fluoride. Table 1 presents the respective melting points and glass transition temperatures of such thermoplastics.

Although US Pat. No. 5,200,009 discloses a shutdown function, the function is provided on the container of the catalytic device, and the container is not adjacent to the catalyst. Therefore, it would take a significant amount of time to transfer the heat of catalysis to the vessel. In other words, catalysis cannot be suppressed quickly. In US Pat. No. 5,300,000, the catalytic device container is melted by the heat of catalysis and physically covers the catalyst for catalysis termination. Therefore, once the shutdown function is activated, the catalyst is physically covered and can no longer carry out the catalytic reaction. Furthermore, after the container melts, the catalyst in the container may leak into the electrolyte, potentially causing a short circuit. In the present invention, firstly, the pore size of the porous membrane (2) is further reduced, or the pores are closed to reduce the gas flow rate. In other words, the present invention does not aim to coat the catalyst itself. Accordingly, catalysis can subsequently continue, providing a battery with long life.

The porous membrane (2) in the present invention has a planar size equal to or greater than that of the catalyst layer (1). Describe functional effects.
The porous membrane (2) can shrink due to the change in volume of the porous membrane (2) due to melting or glass transition. When the porous membrane (2) shrinks and thus has less contact with the catalyst layer (1), the parts of the catalyst layer (1) not covered by the porous membrane (2) and the catalyst layer (1) form a remaining flow path. In this example, not all reactions in the catalyst layer (1) are suppressed, thereby increasing the temperature of the catalyst layer (1) and its surroundings. However, the porous membrane (2) in the present invention has a planar size equal to or greater than that of the catalyst layer (1), and therefore covers the catalyst layer (1) and allows gas to enter the catalyst layer (1) even after heat shrinkage. It can not be easily washed away. Therefore, the temperature rise of the catalyst layer (1) and its surroundings can be suppressed at a higher rate.

Furthermore, in the present invention, the surface of the catalyst layer (1) is in contact with the porous membrane (2). Therefore, when trying to thermally shrink the porous membrane (2), frictional resistance is generated on the contact surface of the catalyst layer (1), suppressing the thermal shrinkage of the porous membrane (2). Furthermore, the porous membrane (2) has a planar size equal to or greater than that of the catalyst layer (1). Therefore, the gas cannot reach the catalyst layer (1) without passing through the porous membrane (2). In order to increase the frictional resistance, a load is applied in the direction of the laminated thickness of the catalyst layer (1) and the porous membrane (2), or the catalyst layer (1) and the porous membrane (2) are laminated together. Can be crimped in any direction.

In one aspect of the invention, the porous membrane (2) can be laminated in contact with both planar surfaces of the catalyst layer (1), or the peripheral portion of the porous membrane (2) is optionally They can be laminated together.
As shown in FIG. 1, two porous membranes (2) can be laminated in contact with both planar surfaces of the catalyst layer (1), namely the top and bottom surfaces. Alternatively, one of the porous membranes can be wrapped around the catalyst layer (1) to form an envelope covering both sides of the catalyst layer (1). A porous membrane (2) is laminated to the top and bottom surfaces of the catalyst layer to increase its resistance to gas flow. Therefore, the gas becomes less likely to flow into the catalyst layer (1), the catalytic action is suppressed, and the temperature rise of the catalyst layer (1) and its surroundings can be reduced at a higher rate.

In addition, the porous membrane (2) has a planar size equal to or greater than that of the catalyst layer (1), so that the upper and lower peripheral portions of the porous membrane (2) can be laminated together. Not only the top and bottom surfaces of the catalyst layer (1), but also its sides can be surrounded by the porous membrane (2). Gas can be prevented from flowing directly to the side of the catalyst layer (1) without passing through the porous membrane (2). Preferably, the sides of the catalyst layer (1) can be in contact with the porous membrane (2). When the catalyst layer (1) is in contact with the porous membrane (2), the heat of catalysis can be easily transferred to the porous membrane (2), thereby pores are more rapidly reduced in size or closed.

In one aspect of the invention, the catalytic device comprises an expanded porous polytetrafluoroethylene membrane (porous ePTFE membrane) (3 ) can be further included.
The Gurley value is evaluated based on JIS P 8117:1998. The Gurley value refers to the time (in seconds) for 100 cm ³ of air to pass vertically through a sample of 6.45 cm ² area at a pressure of 1.29 kPa. The Gurley value is an index of breathability. Even if the porous membrane (2) is destroyed due to heat shrinkage or the like, the porous ePTFE membrane (3) can prevent excessive gas from flowing into the catalyst layer (1). When the porous membrane (2) is melted or undergoes a glass transition, the pores of the porous ePTFE membrane (3) can be reduced in size or closed, such as by melting the porous membrane (2). . Therefore, the porous ePTFE membrane (3) has reduced air permeability, making it difficult for gas to flow into the catalyst layer (1), thereby more reliably suppressing the catalytic action. The Gurley value of the porous ePTFE membrane (3) can be appropriately adjusted according to the catalytic activity of the catalyst layer (1), the predicted amount of generated gas, and the like. A Gurley value of 100 seconds or more can sufficiently reduce the amount of gas flowing to the catalyst layer (1). A porous ePTFE membrane (3) may be provided on either or both of the top and bottom surfaces of the catalyst layer (1).

In one aspect of the invention, the catalytic device may further comprise at least one porous membrane (4) capable of absorbing or decomposing catalyst poisons.
One example of a catalyst poison is dilute sulfuric acid in the electrolyte solution or sulfides produced from dilute sulfuric acid such as _H2S . Catalyst poisons, when in contact with a catalyst, reduce its catalytic performance. Materials that can absorb or decompose catalyst poisons can be activated carbon, ZnO, potassium carbonate, etc., and such materials can absorb or decompose catalyst poisons. Therefore, when the catalytic device includes at least one porous membrane (4) capable of absorbing or decomposing catalyst poisons, deterioration of catalytic performance can be suppressed.

Preferably, the substance capable of absorbing or decomposing catalyst poisons can be contained inside at least one porous membrane (4) capable of absorbing or decomposing catalyst poisons. The phrase "inside the porous membrane (4)" means that a substance capable of absorbing or decomposing catalyst poisons can be present or located inside the cavities of the porous membrane (4) or on the surface of the pores. means In this example, the substance capable of absorbing or decomposing the catalyst poison is exposed within the cavities or on the surface of the pores of the porous membrane (4), readily contacts the catalyst poison, and absorbs or decomposes the catalyst poison. Facilitate.
In at least one porous membrane (4) capable of absorbing or decomposing catalyst poisons, for example polypropylene and expanded polytetrafluoroethylene (ePTFE) can be used, their woven, non-woven, knitted and Porous membranes can also be used. Preferably, the porous membrane (4) may comprise porous ePTFE. Since ePTFE is inherently hydrophobic, the porous membrane (4) allows the water or water vapor produced in the catalyst layer (1) to pass through or repel (repel) the water or water vapor inside the cell. It can promote reflux to the electrolyte solution. A porous membrane (4) containing ePTFE or the like can be subjected to hydrophilization treatment. A metal oxide gel can be used in the hydrophilization treatment. Specifically, a hydrophilic metal oxide sol is provided and the porous member is immersed in the sol and then gelled. In this way, the inner surfaces of the pores of the porous member can be modified by the hydrophilic oxide gel. For example, based on a sol-gel process, the surface of the member can be coated with a silica material for hydrophilization. Such hydrophilization can be performed by surface treatment using plasma or the like. The porous membrane (4) can undergo hydrophilization, thereby increasing its wettability to catalyst poisons. Therefore, the catalyst poison can be absorbed or decomposed more reliably. The degree of hydrophilization can be appropriately set by weighing the backflow action of water generated in the catalyst and the absorption action of catalyst poisons.

At least one of the porous membranes (4) capable of absorbing or decomposing catalyst poisons is prepared by mixing a substance capable of absorbing or decomposing catalyst poisons with polytetrafluoroethylene, and then subjecting the mixture to a porous membrane. It can be made by denaturing or by rendering the mixture porous by stretching. Microcavities defined by nodes and/or fibrils are formed in the polytetrafluoroethylene by stretching a premixed polytetrafluoroethylene with a material capable of absorbing or decomposing the catalyst poison, and A substance capable of absorbing or decomposing catalyst poisons in is retained.

In one aspect of the invention, the catalytic device further comprises a hydrophobic porous membrane (5) located closer to the interior of the lead-acid battery than the catalytic layer (1). The hydrophobic porous membrane (5) can use a porous membrane with high gas permeability so that water vapor is not retained. Gas permeability is high when the Gurley number is 20 seconds or less.
Therefore, the hydrophobic porous membrane (5) does not prevent hydrogen gas and oxygen gas from flowing into the catalyst layer (1). Moreover, the water vapor produced in the catalyst layer (1) can easily flow back into the lead-acid battery and cannot be retained in the catalyst device. Furthermore, the hydrophobic porous membrane (5), which is hydrophobic (water repellent), prevents the sulfuric acid mist and the electrolyte solution (dilute sulfuric acid aqueous solution) from coming into direct contact with the catalyst of the catalyst layer (1), thereby extending the life of the catalyst. can be extended. The hydrophobic porous membrane (5) is preferably non-reactive with other materials inside the cell, such as salts of sulfuric acid. For example, polypropylene and PTFE can be used, as can wovens, nonwovens, knits and porous membranes thereof. The hydrophobic porous membrane (5) is porous polytetrafluoroethylene, as is at least one of the porous ePTFE membrane (3) and the porous membrane (4) capable of absorbing or decomposing catalyst poisons. can be done. Polytetrafluoroethylene, which has excellent properties such as hydrophobicity, chemical resistance, ultraviolet resistance, oxidation resistance, and heat resistance, is suitable as a constituent material for batteries. Alternatively, for example, expandable polytetrafluoroethylene can readily provide the porous member.

At least a portion of the water or water vapor produced by catalysis can absorb or decompose the catalyst layer (1) and porous member (2), and optionally the porous ePTFE membrane (3), catalyst poisons. It can flow back into the lead-acid battery through at least one of the porous membranes (4) and/or the hydrophobic porous membrane (5).

In one aspect of the invention, the catalytic device can include a space in which at least a portion of the water or steam produced can be condensed, and the water or steam produced by catalysis and the space can include a path through which water condensed in can flow back into the interior of the battery. Note that at least part or all of the space can be called a path, and at least part or all of the path can be called a space. FIG. 1A represents an example arrangement: a space in which at least a portion of the water or steam produced can be condensed, and water or steam produced catalytically and condensed in the space. represents the path through which the water that has been removed can return to the interior of the battery.
Further, the catalytic device of the invention as a whole can be gas permeable. Gas permeability can be obtained by adjusting the porosity or packing ratio of the catalyst in the catalyst layer, or the air permeability of the porous membrane. As a result, when the pressure in the battery exceeds a certain value, the gas is discharged from the battery and the pressure in the battery can be lowered. A particular value of pressure can be chosen taking into account the pressure resistance of the cell casing material, or taking into account the gas permeability of parts other than the catalytic device, such as safety valves. As a result, the catalytic device as a whole is gas permeable, which helps improve the explosion protection of the cell, avoid catastrophic damage to the cell, and improve safety.

In one aspect of the invention, the catalytic device of the invention can include essential and optional components housed in a catalytic device casing or spacer. A catalytic device casing or spacer may be formed to define the configuration of the catalytic device and facilitate placement of each component and its attachment to the lead-acid battery. The catalytic device casing or spacer may also be formed to contain spaces in which at least a portion of the water or steam produced may condense. A catalytic device casing or spacer can be formed from a porous member, a membrane member, or the like.
Examples of casings or spacers include casings or spacers made from a resin material such as polypropylene (PP). Examples of porous members include sintered porous members of resin materials such as polypropylene (PP) and expanded porous polytetrafluoroethylene. Examples of membrane members include woven fabrics, non-woven fabrics, knitted fabrics and porous membranes made from resin materials such as polypropylene (PP) and PTFE. The dimensions of the casing or spacers and contained components can be adjusted appropriately so that the porous membrane (2) can be properly loaded to reduce deformation such as thermal shrinkage.

In another aspect of the invention, there is provided a lead-acid battery comprising the catalytic device described above. A lead-acid battery containing a catalytic device can reduce electrolyte solution depletion due to outgassing and leakage from the electrolyte solution, thus providing a long-life lead-acid battery and ensuring safety even with excessive gas flow. can do.

A lead-acid battery can include cells. In this example, each cell can be equipped with a catalytic device of the invention. When a cell is present, catalytically produced water or water vapor from the electrolyte solution in the cell can migrate to other cells. In this example, the amount of electrolyte solution can vary from cell to cell. At least one catalytic device in each cell assists the hydrogen gas and oxygen gas produced in each cell to recombine at the catalyst layer (1) in each cell and the water or water vapor produced in the cell (water or the cell from which the water vapor originates). This helps avoid differences in the amount of electrolyte solution from cell to cell.

In one aspect of the present invention, the catalyst layer (1) can contain a hydrophobic porous member. In the catalyst layer (1), hydrogen gas and oxygen gas generated by cell reactions recombine to produce water or water vapor, and the catalyst layer (1) tends to become moist. When the catalyst is covered with water or steam, hydrogen gas and oxygen gas are less likely to come into contact with the catalyst, which tends to reduce the efficiency of the catalytic reaction (recombination reaction). The hydrophobic porous member in the catalyst layer (1) promotes the release of water or water vapor generated from the catalyst layer (1) and prevents deterioration of catalytic reaction (recombination reaction) efficiency. The hydrophobic porous member also facilitates the flow of generated water or water vapor back into the electrolyte solution inside the cell.

Preferably, in the catalyst layer (1), the catalyst support supporting the catalyst can be placed in the cavity or on the surface of the pores of the catalyst layer (1) (or hydrophobic porous member) (see FIG. 2 sea bream). In this example, the catalyst support, particularly the catalyst, is exposed to the cavities of the catalyst layer (1) and readily comes into contact with hydrogen gas and oxygen gas, promoting the reaction to produce water. When the catalyst layer (1) contains a hydrophobic porous member, the water produced is easily released by the nearby hydrophobic porous member, prolonging the life of the catalyst. The hydrophobic porous member also facilitates the flow of generated water or water vapor back into the electrolyte solution inside the cell.
The catalyst layer (1) can be in forms other than those described above, and the catalyst support can be in the form of powder, molded powder or pelletized powder.

The catalyst layer (1) (or hydrophobic porous member) is preferably non-reactive with other materials inside the cell, such as salts of sulfuric acid. For example, polypropylene and PTFE can be used, as can wovens, nonwovens, knits and porous membranes thereof. The catalyst layer (1) (or hydrophobic porous member) can be porous polytetrafluoroethylene (PTFE). Polytetrafluoroethylene, which inherently has excellent properties such as hydrophobicity, chemical resistance, ultraviolet resistance, oxidation resistance and heat resistance, is suitable as a constituent material for batteries. Porosity can be achieved using blowing agents. Alternatively, for example, expandable polytetrafluoroethylene can readily provide the porous member. More specifically, expanded porous polytetrafluoroethylene is composed of nodes (knots) and fibrils (small fibers). Catalysts or catalyst supports are held in microcavities (micropores) defined by nodes and/or fibrils. Both the nodes and fibrils are made of polytetrafluoroethylene, and the difference is thought to be due to the different states of aggregation or crystallization of polytetrafluoroethylene molecules. It is generally believed that nodes are aggregates of polytetrafluoroethylene primary particles, while fibrils are made up of bundles of crystalline ribbons extending from nodes, or primary particles.

The catalyst layer (1) (or hydrophobic porous member) can be produced by mixing the catalyst support and polytetrafluoroethylene and then making the mixture porous by stretching. By stretching the premixed catalyst support and polytetrafluoroethylene, microcavities defined by nodes and/or fibrils are formed in the polytetrafluoroethylene, within which the catalyst support is retained.
Alternatively, expanded porous PTFE fibers containing the catalyst support and/or the catalyst itself can be made by mixing polytetrafluoroethylene with the catalyst support and/or the catalyst itself and drawing the mixture. Woven fabrics and felts made with fibers can be used as the catalyst layer (1).

The catalyst layer (1) may contain a catalyst carrier that supports the catalyst metal. The catalytic metal can be any catalyst for recombination of hydrogen and oxygen to produce water, examples include Pd, Pt and Au. The carrier that supports the catalyst can be any carrier that has sufficient specific surface area to support the catalyst in the desired state of dispersion. The support may be selected from the group consisting of silica, alumina, zeolites, carbon, group IVB, group VB, group VIB, group VIIB and group VIII transition metal oxides and carbides and combinations thereof. . Alternatively, the support can be a carbon material. It is undesirable for the carrier material to undergo chemical reactions other than the desired reaction, or for the substances that make up the carrier material to be leached out upon contact with condensed water. In this respect, carbon materials are chemically stable and are preferred support materials. Examples of carbon materials include carbon black (eg, oil furnace black, channel black, lamp black, thermal black and acetylene black), activated carbon, coke, natural graphite and artificial graphite. They can be used in combination.

The present invention will now be described in more detail with reference to examples and comparative examples. However, the following examples should not be construed as limiting the invention.

(Example 1)
Catalyst layer (1) was provided as follows. A catalyst layer (1) was provided by providing 5% by mass of Pd catalyst/activated carbon-supported catalyst, mixing the catalyst with an alumina filler (filling rate of 70% by mass), and sintering. As the porous membrane (2), two polyethylene porous membranes (melting point: 130° C.) having a planar size larger than that of the catalyst layer (1) were provided. A catalytic device casing was provided with recessed portions to accommodate the surfaces of the catalytic layer (1) and porous membrane (2). The catalyst layer (1) was sandwiched between the porous membranes (2) so that the surface of the catalyst layer (1) was in contact with the surface of each porous membrane (2) and housed in the recessed portion of the catalyst device casing. The resulting catalytic device was mounted in a chamber provided to simulate a lead-acid battery. No electrolyte solution was used. Instead, hydrogen gas and oxygen gas were fed to the catalytic device. Oxygen and hydrogen were supplied in a ratio of 1:2 according to the stoichiometric ratio. Hydrogen was supplied at flow rates ranging from 57 ml/min (equivalent to 5 A) to 226 ml/min (equivalent to 20 A). In Example 1, the temperature of the catalyst layer (1) was about 100° C. at most even when hydrogen was continuously flowed at 226 ml/min (corresponding to 20 A) for 5 minutes or more. Therefore, the porous membrane (2) did not melt and the catalytic reaction continued, allowing oxygen and hydrogen to recombine to produce water.
Furthermore, the above experiment was reproduced using two porous membranes (2)' of polyethylene of the same planar size as the catalyst layer (1) instead of the porous membrane (2). As a result, the experimental results for porous membrane (2)' were the same as those for porous membrane (2).

As a comparative example, a catalyst device was provided in which only the catalyst layer (1) was accommodated in the catalyst device casing. In other words, the catalytic device did not comprise a porous membrane (2). When hydrogen and oxygen were supplied to the catalytic device, the temperature of the catalytic layer (1) exceeded 150° C. after supplying 57 ml/min (corresponding to 5 A) of hydrogen for 10 minutes. Such temperature exceeded the melting point of polyethylene as the material of the porous membrane (2).

As another comparative example, catalyst layer (1) and porous membrane (2) were placed in a recessed portion of the catalyst device casing such that the surface of catalyst layer (1) was not in contact with the surface of each porous membrane (2). accommodated in. The order of lamination of catalyst layer (1) and porous membrane (2) was the same as in Example 1. Therefore, there was a space between the catalyst layer (1) and the porous membrane (2). When hydrogen and oxygen were supplied to the catalyst device, the temperature of the catalyst layer (1) exceeded 150° C. and the porous membrane (2) melted after supplying 170 ml/min (corresponding to 15 A) of hydrogen. It was thought that the reason was that the porous membrane (2) was not in contact with the catalyst layer (1) and therefore no frictional resistance acted between them. Therefore, the porous membrane (2) is thermally shrunk to allow oxygen and hydrogen to reach the catalyst layer (1) without passing through the porous membrane (2), thereby promoting the catalytic reaction and increasing the temperature. rice field.

(Example 2)
Using the catalytic device provided in Example 1, it was determined to what extent the water produced by recombination due to the catalytic reaction backflowed. Hydrogen and oxygen were supplied to the catalytic device attached to the chamber at a rate of 2.7 ml/min and 1.8 ml/min respectively at 60°C.
The backflow performance of a catalytic component is determined by the amount (%) of water collected in the chamber after testing, based on the amount of water or water vapor that can be produced when all the oxygen and hydrogen supplied react and recombine. stipulated.
In Example 2, the backflow performance was 70%. In other words, the amount of water collected in the chamber was 70%. The amount of water remaining in the catalytic device was 0%.
As a reference example, the product based on Patent Document 2 had a backflow performance of 50% under the same conditions as in Example 2. Here, 4% of the backflow performance was due to water remaining in the product.

After the above tests were completed, the catalytic devices were stored in an environment with a temperature of 30° C. and tested again in the same manner as above. No decrease in backflow performance was observed in the catalyst device of the present invention. As a reference example, in the product based on Patent Document 2, the backflow performance decreased to about 20% of the value before storage. This is because it is desirable to control the temperature to a relatively high temperature (approximately 70 to 90° C.) in the products of Reference Examples.

(Example 3)
Two expanded porous polytetrafluoroethylene membranes (3) having a Gurley number of 100 seconds or greater and in contact with the porous membrane (2) on the side opposite the catalyst layer (1) were applied to the catalyst provided in Example 1. Further housed in the device. Hydrogen and oxygen were fed under the same conditions as in Example 1. The results obtained with the catalytic device of Example 3 were similar to those of Example 1. In other words, even when 226 ml/min (corresponding to 20 A) of hydrogen was continued to flow for 5 minutes or more, the temperature of the catalyst layer (1) was at most about 100°C. Therefore, the porous membrane (2) did not melt and the catalytic reaction could continue, thereby recombining oxygen and hydrogen to produce water. Furthermore, when the amount of hydrogen supplied to the catalytic device of Example 1 was increased to 283 ml/min (equivalent to 25 A), a temperature increase of several degrees was observed. Little increase in temperature was observed when the amount of hydrogen supplied to the catalytic device of Example 3 was increased to 283 ml/min (equivalent to 25 A). In Example 3, in which the stretched porous polytetrafluoroethylene membrane (3) was lowered, it was confirmed that the effect of reducing the temperature rise was exhibited to a greater extent.

(Example 4)
In Examples 1-3, polyethylene was used as the material for the porous membrane (2). Not only such porous membranes, but also porous membranes made from polyethylene, polypropylene, polyvinyl chloride, polymethyl methacrylate, polystyrene or polyvinylidene fluoride as materials were provided. The Gurley value of each of these porous membranes was measured at room temperature. These porous membranes were then stored above the melting point/glass transition temperature of the respective materials and their Gurley numbers were measured again. All porous membranes increased the Gurley number to about twice the value measured at room temperature. From this result, it was confirmed that porous membranes made of materials other than polyethylene can also be used as the porous membrane (2) in the present invention.

Claims (10)

a catalyst layer containing a catalyst for promoting a reaction for producing water or steam from oxygen and hydrogen; and a porous membrane containing polyethylene having a melting point of 160° C. or less;
A catalytic device for a lead-acid battery comprising:
A catalyst device, wherein at least one surface of the catalyst layer is in contact with the porous membrane, and the porous membrane has a planar size equal to or larger than that of the catalyst layer. 2. The catalytic device of claim 1, comprising at least two said porous membranes, said porous membranes being laminated in contact with both planar surfaces of said catalyst layer. 3. The catalytic device of claim 2, wherein peripheral portions of said porous membrane are laminated together . 4. The method according to any one of claims 1 to 3, further comprising an expanded porous polytetrafluoroethylene membrane having a Gurley number of 100 seconds or more and being in contact with the porous membrane on the opposite side of the catalyst layer. catalytic device. 5. The catalytic device of claim 4 , further comprising at least one porous membrane capable of absorbing or decomposing catalyst poisons in contact with said expanded porous polytetrafluoroethylene membrane on the opposite side of said porous membrane. . 6. The porous membrane capable of absorbing or decomposing the catalyst poison includes a substance capable of absorbing or decomposing the catalyst poison inside the porous membrane capable of absorbing or decomposing the catalyst poison. catalytic device. 7. A catalytic device according to claim 5 or 6, wherein the porous membrane capable of absorbing or decomposing catalyst poisons comprises expanded polytetrafluoroethylene. 8. The method according to any one of claims 1 to 7, further comprising a hydrophobic porous membrane located closer to the inside of the lead-acid battery than the catalyst layer, wherein the hydrophobic porous membrane has a Gurley number of 20 seconds or less. catalytic device. 9. The catalytic device of claim 8, wherein said hydrophobic porous membrane comprises expanded polytetrafluoroethylene. A lead-acid battery comprising the catalytic device according to any one of claims 1-9.

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